This invention relates to a heat-sealable laminated polyester film. More particularly, the present invention relates to a heat-sealable laminated polyester film which preeminently excels in heat-sealing strength and also excels in workability.
The polyester film generally is excellent in strength and heat-resistance but is deficient in heat-sealability. When it is used for packaging, electric insulation, or industry in general, it must be given heat-sealability.
Heretofore in the fields of use mentioned above, films having a varying heat-sealable layer on one surface of a polyester film by the technique of lamination or the technique of coating have found utility. However, it is difficult by the coating technique to obtain sufficient heat-sealing strength of the produced film. In the case of the technique laminating another film, sufficient heat-sealing strength is not obtained by simply laminating a copolyester film of low crystallinity. When a film of other material than polyester is used for the lamination, this technique has the disadvantage that the process of molding is complicated and the production is unduly expensive. Particularly in recent years, a heat-sealable polyester film possessing high heat-sealing strength and warranting perfect safety as the material for lids in C-PET containers which are intended for use in electric ovens and the other ovens has been desired.
The present inventors have continued a diligent study in search of a way of fulfilling this desirability, to find that a laminated film of a specific layer composition possesses preeminent heat-sealing strength. Thus the present invention has been accomplished based on this finding.